i have had issue when pumping boiling or near boiling temps through my chugger. The pump cavitates (basically boils the water on the low pressure side of the impeller blades) and looses prime. I've found that to overcome this i have to throttle the output back a ways and SLOWLY bring it up.

I have my entire pump rotated 90 deg. from how yours is so that the fluid comes up from the bottom; then I have a "T" on the top (out side) with a manual bleeder valve out the side of the "T" and another valve going up towards whatever. This way I am sure that any air trapped in the pump head travels upward and out.

I'll open the purge valve, with the top valve still closed, until liquid comes out the side, to ensure the pump head is full; then I'll turn the pump on, close the purge valve and slowly open the top valve. It seems to work every time.

I'm not positive this will help, but it works for me and many others I have seen on here. Four batches this way and has worked great.

+1 The schematic shows a dump valve. Use it to purge the air from the input line and the pump head then give it another try. IMO, the problem is that the pump is not properly primed. I don't use an auto-vent gizmo, so I cannot advise on where to position it. You should be able to manually prime the pump with or without the autovent installed.

The side-to-side orientation is just fine and probably a bit better in fact. The water flow into the inlet at the center of the pump, not "from the bottom". This is a common misquote. The liquid then exits at the root of the outlet connection. For example, in Flomaster's pic, the exit of the pump chamber is actually on the side of the pump not the top. If Flomaster's pump were rotated 90º clockwise, the the exit would be top dead center.

Either way it doesn't matter; both configurations work just fine and have virtually no difference in performance. The only way that is less than desirable is to have the pump side-to-side with the exit on the bottom. If you have it that way change it.

Your autovent is not configured in the typical way. It should still work their though... However, there is a small chance that because of the position of your autovent it is not receiving enough positive pressure to fully close and is allowing atmospheric pressure to access the high pressure side of your pump. This would kill it.

Why are you using the autovents? If you have a dump valve just use that to prime and remove the autovent??? When you set up your system, open the ball valve fully at your kettle, then open the dump valve. Once a good flow starts with the pump off, shut the dump valve. Start the pump. Prosper.

I spoke to Mike at Chugger Pumps and he is sending me a new head to try out.

He also mentioned that it could be a problem with the quick disconnects that I'm using. Everything in my system is 1/2", but they have 3/8" couplings.

I'm hoping that isn't the problem because I am planning on whirlpooling through my CFC using this pump and if some smaller couplings are stopping the pump, then the 1/2" copper tubing that I used in the chiller will definitely be a problem. . .

I will post my findings when I have a chance to try out the new head.

As an aside, Mike was extremely nice and helpful. You really couldn't ask for a more responsive company.